MRAM having memory cell array in which cross-point memory cells are arranged by hierarchical bit line scheme and data read method thereof

Abstract

A memory cell array is of a hierarchical bit line scheme in which cross-point memory cells that exhibit a magnetoresistive effect are laid out in a matrix, and a read bit line to be used in a data read mode is constituted by a main bit line and a sub bit line. A column select circuit selects a main bit line and connects it to a sense amplifier. A row select circuit selects a word line for each cell unit, and in read operation, sets, in a floating state, word lines to which unselected memory cells connected to the sub bit line to which a selected memory cell is connected are connected, and sets the remaining word lines connected to sub bit lines which do not include the selected memory cell to a potential substantially equal to the main bit line.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2003-144792, filed May 22, 2003, the entire contents of which are incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates to a magnetic random access memory (MRAM) which stores binary information using the magnetoresistive effect, and a data read method thereof and, more particularly, to potential control of main / sub bit lines and word lines in the read mode of a memory cell array in which cross-point memory cells are arranged by a divided bit line structure (hierarchical bit line scheme).[0004]2. Description of the Related Art[0005]MRAMs are devices which perform memory operation by storing binary information using the magnetoresistive effect. They are regarded as one of candidates for universal storage devices that can realize all the nonvolatility, high i...

AI Technical Summary

Benefits of technology

[0014]According to still another aspect of the invention, there is provided a magnetic random access memory comprising a memory cell array of hierarchical bit line scheme in which cross-point memory cells that exhibit a magnetoresistive effect are laid out in a matrix, and a read bit line to be used in a data read mode is constituted by a main bit line and a sub bit line, connection means for selectively connecting a word line connected to a cross-point memory cell to be selected to one of first and second potential supply sources which are different from each other, and control means for controlling the connection means to selectively connect the word line and to set a further word line in an electrically floating state, wherein the control means comprises first and second row decoders and word line drivers to set a potential of the word line in the read mode, and when the connection means is deactivated by the first and second row decoders and word line drivers, the further word line is set in the electrically floating state.

Problems solved by technology

How to ensure the read margin presents a significant challenge in implementing MRAMs.

The practical utility is believed to be still insufficient at present.

Hence, it is difficult to increase the capacity or the degree of integration.

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